Lane departure preventing device

ABSTRACT

A lane departure preventing device includes at least one electronic control unit. The at least one electronic control unit is configured to: when there is a likelihood that a vehicle will depart from a traveling lane, calculate a prevention yaw moment, and control a brake actuator such that the prevention yaw moment is applied to the vehicle; acquire a lateral acceleration; determine whether the lateral acceleration is greater than an ideal value by a predetermined value; control the brake actuator such that the braking force matches a target braking force required to apply the prevention yaw moment to the vehicle, when the lateral acceleration is not greater than the ideal value by the predetermined value; and control the brake actuator such that the braking force is less than the target braking force, when the lateral acceleration is greater than the ideal value by the predetermined value.

INCORPORATION BY REFERENCE

This application is a continuation application of U.S. application Ser.No. 15/787,015, filed on Oct. 18, 2017, which is based on and claimspriority under 35 U.S.C. § 119 to Japanese Patent Application No.2016-208547, filed on Oct. 25, 2016, the disclosures of which areincorporated by reference herein in their entireties.

BACKGROUND 1. Technical Field

The present disclosure relates to a lane departure preventing device.

2. Description of Related Art

As a lane departure preventing device, a lane departure preventingdevice that applies a prevention yaw moment (that is, a target yawmoment) capable of preventing departure of a vehicle from a travelinglane to the vehicle by controlling braking forces applied to vehiclewheels when there is a likelihood that the vehicle will depart from thetraveling lane is known (for example, see Japanese Patent ApplicationPublication No. 2006-182308 (JP 2006-182308 A)).

SUMMARY

Depending on a state of a vehicle to which a prevention yaw moment isapplied, it may not be preferable to continue to apply an originalprevention yaw moment which has been calculated to prevent departure ofa vehicle from a traveling lane. Specifically, when a prevention yawmoment is applied to the vehicle, an acceleration of the vehicle(specifically, a longitudinal acceleration and a lateral acceleration)varies. When the acceleration state of the vehicle does not match motioncharacteristics of the vehicle, there is a likelihood that a certainabnormality will occur internally or externally in the vehicle. Sincethe original prevention yaw moment is calculated without considering anabnormality occurring in the vehicle, it is not preferable to continueto apply the original yaw moment when an abnormality occurs in thevehicle. However, in JP 2006-182308 A, the original prevention yawmoment continues to be applied to the vehicle until departure of thevehicle from the traveling lane is avoided. Accordingly, the lanedeparture preventing device described in JP 2006-182308 A cannotappropriately determine whether the original prevention yaw moment willcontinue to be applied depending on the vehicle state.

The disclosure provides a lane departure preventing device that canappropriately determine whether a prevention yaw moment will continue tobe applied depending on a vehicle state and can apply the prevention yawmoment.

A lane departure preventing device includes at least one electroniccontrol unit. The at least one electronic control unit is configured towhen there is a likelihood that a vehicle will depart from a travelinglane in which the vehicle travels, calculate a prevention yaw moment forpreventing departure of the vehicle from the traveling lane, and controla brake actuator configured to apply a braking force to a vehicle wheelsuch that the prevention yaw moment is applied to the vehicle. The atleast one electronic control unit is configured to acquire a firstlateral acceleration and a longitudinal acceleration generated in thevehicle when the prevention yaw moment is applied. The at least oneelectronic control unit is configured to determine whether the firstlateral acceleration is greater than an ideal value of the first lateralacceleration by a first predetermined value. The ideal value of thefirst lateral acceleration is estimated, from motion characteristics ofthe vehicle, to be generated in the vehicle due to application of theprevention yaw moment when the longitudinal acceleration is generated inthe vehicle due to application of the prevention yaw moment. The atleast one electronic control unit is configured to control the brakeactuator such that the braking force matches a target braking forcerequired to apply the prevention yaw moment to the vehicle, when it isdetermined that the first lateral acceleration is not greater than theideal value by the first predetermined value, and control the brakeactuator such that the braking force is less than the target brakingforce, when it is determined that the first lateral acceleration isgreater than the ideal value by the first predetermined value.

According to this configuration, when the lateral acceleration isgreater than the ideal value of the lateral acceleration, which isestimated from the longitudinal acceleration, by the first predeterminedvalue, it is determined that a certain abnormality occurs internally orexternally in the vehicle. When the lateral acceleration is greater thanthe ideal value by the first predetermined value (that is, when anabnormality occurs in the vehicle), it is determined that it is notpreferable to continue to apply the original prevention yaw moment whichhas been calculated to prevent departure of the vehicle from thetraveling lane. Accordingly, the braking force applied to the vehiclewheel is decreased instead of continuously applying the originalprevention yaw moment. As a result, the lane departure preventing devicecan appropriately determine whether to continue to apply the preventionyaw moment depending on a vehicle state.

The at least one electronic control unit may be configured to cancelapplication of the braking force by the brake actuator when it isdetermined that the first lateral acceleration is greater than the idealvalue by the first predetermined value.

According to this configuration, when it is estimated that anabnormality occurs in the vehicle, continuous application of theoriginal prevention yaw moment is appropriately stopped.

The at least one electronic control unit may be configured to determinewhether a total value of the first lateral acceleration and a secondlateral acceleration is greater than the ideal value by a secondpredetermined value greater than the first predetermined value, whenapplication of the prevention yaw moment is started in a state in whichthe second lateral acceleration is generated in the vehicle, anddetermine whether the first lateral acceleration is greater than theideal value by the first predetermined value when application of theprevention yaw moment is started in a state in which the second lateralacceleration is not generated in the vehicle. The at least oneelectronic control unit may be configured to control the brake actuatorsuch that the braking force matches the target braking force when it isdetermined that the total value of the first lateral acceleration andthe second lateral acceleration is not greater than the ideal value bythe second predetermined value, and control the brake actuator such thatthe braking force is less than the target braking force when it isdetermined that the total value of the first lateral acceleration andthe second lateral acceleration is greater than the ideal value by thesecond predetermined value.

According to this configuration, as will be described later in detailwith reference to the accompanying drawings, even when application ofthe prevention yaw moment is started in a state in which a lateralacceleration is generated in the vehicle, the lane departure preventingdevice can appropriately determine whether to continue to apply theprevention yaw moment depending on the vehicle state.

The second predetermined value may be greater than the firstpredetermined value by the second lateral acceleration generated in thevehicle before application of the prevention yaw moment is started

According to this configuration, even when application of the preventionyaw moment is started in a state in which a lateral acceleration isgenerated in the vehicle, the lane departure preventing device canappropriately determine whether to continue to apply the prevention yawmoment depending on the vehicle state.

The at least one electronic control unit may be configured to cancelapplication of the braking force by the brake actuator when it isdetermined that the total value of the first lateral acceleration andthe second lateral acceleration is greater than the ideal value by thesecond predetermined value.

According to this configuration, when it is estimated that anabnormality occurs in the vehicle, continuous application of theoriginal prevention yaw moment is appropriately stopped.

The first predetermined value may be calculated based on thelongitudinal acceleration.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a block diagram illustrating a configuration of a vehicleaccording to an embodiment;

FIG. 2 is a flowchart illustrating a flow of a lane departure preventingoperation;

FIG. 3A is a graph illustrating a relationship between a longitudinalacceleration and a lateral acceleration when an abnormality does notoccur in a vehicle to which a prevention yaw moment is applied;

FIG. 3B is a graph illustrating an example of abnormality conditionswhich are determined based on a longitudinal acceleration and a lateralacceleration;

FIG. 3C is a graph illustrating an example of abnormality conditionswhich are determined based on a longitudinal acceleration and a lateralacceleration;

FIG. 3D is a graph illustrating an example of abnormality conditionswhich are determined based on a longitudinal acceleration and a lateralacceleration;

FIG. 4 is a flowchart illustrating a flow of a lane departure preventingoperation according to a first embodiment;

FIG. 5 is a flowchart illustrating a flow of a lane departure preventingoperation according to a third embodiment; and

FIG. 6 is a graph illustrating abnormality conditions which are used inthe third embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a lane departure preventing device according to embodimentsof the disclosure will be described with reference to the accompanyingdrawings. In the following description, description will be made using avehicle 1 in which the lane departure preventing device according to theembodiments of the disclosure is mounted.

(1) Configuration of Vehicle 1 According to First Embodiment (1-1)

A configuration of a vehicle 1 according to a first embodiment will bedescribed below with reference to the block diagram illustrated inFIG. 1. As illustrated in FIG. 1, the vehicle 1 includes a brake pedal111, a master cylinder 112, a brake pipe 113FL, a brake pipe 113RL, abrake pipe 113FR, a brake pipe 113RR, a front-left wheel 121FL, arear-left wheel 121RL, a front-right wheel 121FR, a rear-right wheel121RR, a wheel cylinder 122FL, a wheel cylinder 122RL, a wheel cylinder122FR, a wheel cylinder 122RR, a brake actuator 13, a steering wheel141, a vibration actuator 142, a vehicle speed sensor 151, a wheel speedsensor 152, a yaw rate sensor 153, an acceleration sensor 154, a camera155, a display 161, a speaker 162, and an electronic control unit (ECU)17 which is a specific example of a “lane departure preventing device.”

The brake pedal 111 is a pedal which is depressed by a driver to brakethe vehicle 1. The master cylinder 112 adjusts a pressure of a brakefluid (or an arbitrary fluid) in the master cylinder 112 to a pressurecorresponding to an amount of depression of the brake pedal 111. Thepressure of the brake fluid in the master cylinder 112 is transmitted tothe wheel cylinders 122FL, 122RL, 122FR, and 122RR via the brake pipes113FL, 113RL, 113FR, and 113RR. Accordingly, braking forcescorresponding to the fluid pressures of the brake fluid transmitted tothe wheel cylinders 122FL, 122RL, 122FR, and 122RR are applied to thefront-left wheel 121FL, the rear-left wheel 121RL, the front-right wheel121FR, and the rear-right wheel 121RR.

The brake actuator 13 can adjust the pressures of the brake fluidtransmitted to the wheel cylinders 122FL, 122RL, 122FR, and 122RRregardless of the amount of depression of the brake pedal 111 under thecontrol of the ECU 17. Accordingly, the brake actuator 13 can adjust thebraking forces applied to the front-left wheel 121FL, the rear-leftwheel 121RL, the front-right wheel 121FR, and the rear-right wheel 121RRregardless of the amount of depression of the brake pedal 111.

The steering wheel 141 is an operator that is operated by a driver tosteer the vehicle 1 (that is, to steer turning wheels). In the firstembodiment, the turning wheels are assumed to be the front-left wheel121FL and the front-right wheel 121FR. The vibration actuator 142 cancause the steering wheel 141 to vibrate under the control of the ECU 17.

The vehicle speed sensor 151 detects a vehicle speed Vv of the vehicle1. The wheel speed sensor 152 detects wheel speeds Vw of the front-leftwheel 121FL, the rear-left wheel 121RL, the front-right wheel 121FR, andthe rear-right wheel 121RR. The yaw rate sensor 153 detects a yaw rate yof the vehicle 1. The acceleration sensor 154 detects an acceleration G(specifically, a longitudinal acceleration Gx and a lateral accelerationGy) of the vehicle 1. The camera 155 is an imaging device that images anexternal situation of the front side of the vehicle 1. Detection dataindicating the detection results of the vehicle speed sensor 151 to theacceleration sensor 154 and image data indicating an image captured bythe camera 155 are output to the ECU 17.

The display 161 can display arbitrary information under the control ofthe ECU 17. The speaker 162 can output an arbitrary sound under thecontrol of the ECU 17.

The ECU 17 controls the whole operations of the vehicle 1. In the firstembodiment, particularly, the ECU 17 performs a lane departurepreventing operation for preventing departure of the vehicle 1 from atraveling lane in which the vehicle is traveling. Accordingly, the ECU17 serves as a controller for realizing so-called lane departure alert(LDA) or lane departure prevention (LDP).

In order to perform the lane departure preventing operation, the ECU 17includes a data acquiring unit 171, an LDA control unit 172, and an LDAlimiting unit 173, as processing blocks which are logically realized orprocessing circuits which are physically realized in the ECU 17. Theoperations of the data acquiring unit 171, the LDA control unit 172, andthe LDA limiting unit 173 will be described later in detail withreference to FIG. 2 and the like, and outlines thereof will be describedbelow in brief The data acquiring unit 171 acquires the detection dataindicating the detection results of the vehicle speed sensor 151 to theacceleration sensor 154 and the image data indicating an image capturedby the camera 155. When there is a likelihood that the vehicle 1 willdepart from the traveling lane in which the vehicle is traveling basedon the detection data and the image data acquired by the data acquiringunit 171, the LDA control unit 172 controls the brake actuator 13 suchthat a prevention yaw moment capable of preventing departure of thevehicle 1 from the traveling lane using the braking force is applied toat least one of the front-left wheel 121FL, the rear-left wheel 121RL,the front-right wheel 121FR, and the rear-right wheel 121RR. “Preventionof departure of the vehicle 1 from the traveling lane” in the firstembodiment means that an actual departure distance of the vehicle 1 fromthe traveling lane when a prevention yaw moment is applied is set to beless than a departure distance of the vehicle 1 from the traveling lanewhich is assumed when the prevention yaw moment is not applied. The LDAlimiting unit 173 determines whether to stop application of theprevention yaw moment (that is, whether to stop application of thebraking force capable of applying the prevention yaw moment).

(1-2) Details of Lane Departure Preventing Operation

A lane departure preventing operation which is performed by the ECU 17will be described below with reference to the flowchart illustrated inFIG. 2.

As illustrated in FIG. 2, first, the data acquiring unit 171 acquiresthe detection data indicating the detection results of the vehicle speedsensor 151 to the acceleration sensor 154 and the image data indicatingan image captured by the camera 155 (Step S10).

Thereafter, the LDA control unit 172 specifies a lane edge of thetraveling lane (a white line is used as an example of the lane edge inthe first embodiment) in which the vehicle 1 is traveling in an imagecaptured by the camera 155 by analyzing the image data acquired in StepS10 (Step S20).

Thereafter, the LDA control unit 172 calculates a radius of curvature Rof the traveling lane in which the vehicle 1 is traveling based on thewhite line specified in Step S20 (Step S21). The radius of curvature Rof the traveling lane is actually equivalent to a radius of curvature ofthe white line. Accordingly, the LDA control unit 172 may calculate theradius of curvature of the white line specified in Step S20 and treatthe calculated radius of curvature as the radius of curvature R of thetraveling lane. Here, the LDA control unit 172 may calculate the radiusof curvature R of the traveling lane in which the vehicle 1 is travelingusing position information of the vehicle 1 specified using a globalpositioning system (GPS) and map information used for a navigationoperation.

The LDA control unit 172 calculates a current lateral position X of thevehicle 1 based on the white line specified in Step S20 (Step S22). The“lateral position X” in the first embodiment indicates a distance fromthe center of the traveling lane to the vehicle 1 in a lane widthdirection perpendicular to an extending direction of the traveling lane(a lane extending direction) (typically a distance to the center of thevehicle 1). In this case, it is preferable that one of a direction tothe right side from the center of the traveling lane and a direction tothe left side be set as a positive direction and the other of thedirection to the right side from the center of the traveling lane andthe direction to the left side be set as a negative direction. The sameis true of a lateral velocity V1 which will be described later, a yawmoment such as the above-mentioned prevention yaw moment, theabove-mentioned lateral acceleration Gy, and the above-mentioned yawrate γ, and the like.

The LDA control unit 172 additionally calculates a departure angle θ ofthe vehicle 1 based on the white line specified in Step S20 (Step S22).The “departure angle θ” in the first embodiment indicates an angle whichis formed by the traveling lane and a front-rear direction axis of thevehicle 1 (that is, an angle formed by the white line and the front-reardirection axis of the vehicle 1).

The LDA control unit 172 calculates the lateral velocity V1 of thevehicle 1 based on time-series data of the lateral position X of thevehicle 1 calculated from the white line (Step S22). Here, the LDAcontrol unit 172 may calculate the lateral velocity V1 of the vehicle 1based on at least one of the detection result of the vehicle speedsensor 151, the calculated departure angle θ, and the detection resultof the acceleration sensor 154. The “lateral velocity V1” in the firstembodiment indicates the speed of the vehicle 1 in the lane widthdirection.

The LDA control unit 172 sets an allowable departure distance D (StepS23). The allowable departure distance D indicates a maximum value of adeparture distance of the vehicle 1 from the traveling lane (that is, adeparture distance of the vehicle 1 from the white line) when thevehicle 1 departs from the traveling lane. Accordingly, the lanedeparture preventing operation is an operation of applying a preventionyaw moment to the vehicle 1 such that the departure distance of thevehicle 1 from the traveling lane is less than the allowable departuredistance D.

The LDA control unit 172 may set the allowable departure distance D fromthe viewpoint of satisfying requirements of the law (for example,requirements of a new car assessment programme (NCAP)). In this case,the allowable departure distance D set from the viewpoint of satisfyingthe requirements of the law may be used as a default allowable departuredistance D.

Thereafter, the LDA control unit 172 determines whether there is alikelihood that the vehicle 1 will depart from the traveling lane inwhich the vehicle is traveling (Step S24). Specifically, the LDA controlunit 172 calculates a future lateral position Xf. For example, the LDAcontrol unit 172 calculates the lateral position X at a time point atwhich the vehicle 1 travels a distance corresponding to a front gazedistance from the current position as the future lateral position Xf.The future lateral position Xf can be calculated by adding orsubtracting a value, which is obtained by multiplying a time Δt requiredfor the vehicle 1 to travel the front gaze distance by the lateralvelocity V1, to or from the current lateral position X. Thereafter, theLDA control unit 172 determines whether the absolute value of the futurelateral position Xf is equal to or greater than a departure thresholdvalue. When it is assumed that the vehicle 1 travels in a directionparallel to the lane extending direction, the departure threshold valueis, for example, a value (specifically (width of traveling lane−width ofvehicle 1)/2)) which is determined based on the width of the travelinglane and the width of the vehicle 1. In this case, a situation in whichthe absolute value of the future lateral position Xf is equal to thedeparture threshold value corresponds to a situation in which a sidesurface of the vehicle 1 along the lane width direction (for example, aside surface distant from the center of the traveling lane) is locatedon the white line. A situation in which the absolute value of the futurelateral position Xf is greater than the departure threshold value is asituation in which a side surface of the vehicle 1 along the lane widthdirection (for example, a side surface distant from the center of thetraveling lane) is located outside the white line. Accordingly, when theabsolute value of the future lateral position Xf is not equal to orgreater than the departure threshold value, the LDA control unit 172determines that there is not likelihood that the vehicle 1 will departfrom the traveling lane in which the vehicle is traveling. On the otherhand, when the absolute value of the future lateral position Xf is equalto or greater than the departure threshold value, the LDA control unit172 determines that there is a likelihood that the vehicle 1 will departfrom the traveling lane in which the vehicle is traveling. Here, sincethe vehicle 1 may actually travel in a direction which is not parallelto the lane extending direction, an arbitrary value other than theabove-mentioned threshold value may be used as the departure thresholdvalue.

The above-mentioned operation is merely an example of an operation ofdetermining whether there is a likelihood that the vehicle 1 will departfrom the traveling lane in which the vehicle is traveling. Accordingly,the LDA control unit 172 may determine whether there is a likelihoodthat the vehicle 1 will depart from the traveling lane in which thevehicle is traveling using an arbitrary criterion. An example of thesituation in which “there is a likelihood that the vehicle 1 will departfrom the traveling lane” is a situation in which the vehicle 1 will goover or come in contact with the white line in the near future (forexample, at a time point at which the vehicle travels a distancecorresponding to the front gaze distance).

When it is determined in Step S24 that there is no likelihood that thevehicle 1 will depart the traveling lane (NO in Step S24), the lanedeparture preventing operation illustrated in FIG. 2 ends. Accordingly,the operations (Steps S25 to S32) which are performed when it isdetermined that there is a likelihood that the vehicle 1 will departfrom the traveling lane are not performed. That is, the LDA control unit172 controls the brake actuator 13 such that the prevention yaw momentis not applied to the vehicle 1 (that is, such that a braking forcecapable of applying the prevention yaw moment to the vehicle 1 is notapplied). The LDA control unit 172 does not alarm a driver about thatthere is a likelihood that the vehicle 1 will depart from the travelinglane.

When the lane departure preventing operation illustrated in FIG. 2 endsbecause it is determined that there is no likelihood that the vehicle 1will depart from the traveling lane, the ECU 17 starts the lanedeparture preventing operation illustrated in FIG. 2 again after a firstpredetermined period of time (for example, several milliseconds toseveral tens of milliseconds) elapses. That is, the lane departurepreventing operation illustrated in FIG. 2 is repeatedly performed atintervals corresponding to the first predetermined period of time. Thefirst predetermined period of time is a period corresponding to adefault period in which the lane departure preventing operationillustrated in FIG. 2 is repeatedly performed.

On the other hand, when it is determined in Step S24 that there is alikelihood that the vehicle 1 will depart from the traveling lane (YESin Step S24), the LDA control unit 172 warns a driver about that thereis a likelihood that the vehicle 1 will depart from the traveling lane(Step S25). For example, the LDA control unit 172 may control thedisplay 161 such that an image indicating that there is a likelihoodthat the vehicle 1 will depart from the traveling lane is displayed.Alternatively, for example, in addition to or instead of controlling ofthe display 161 as described above, the LDA control unit 172 may controlthe vibration actuator 142 such that the driver is notified that thereis a likelihood that the vehicle 1 will depart from the traveling laneby vibration of the steering wheel 141. Alternatively, in addition to orinstead of controlling of at least one of the display 161 and thevibration actuator 142 as described above, the LDA control unit 172 maycontrol the speaker (a so-called buzzer) 162 such that the driver isnotified that there is a likelihood that the vehicle 1 will depart fromthe traveling lane by warning sound.

When it is determined that there is a likelihood that the vehicle 1 willdepart from the traveling lane, the LDA control unit 172 additionallycontrols the brake actuator 13 such that the braking force capable ofapplying the prevention yaw moment to the vehicle 1 is applied (StepsS26 to S29).

Specifically, when there is likelihood that the vehicle 1 will departfrom the traveling lane, there is a high likelihood that the vehicle 1will travel to be separated away from the center of the traveling lane.Accordingly, when a traveling path of the vehicle 1 is changed from atraveling path in which the vehicle travels to be separated away fromthe center of the traveling lane to a traveling path in which thevehicle travels toward the center of the traveling lane, departure ofthe vehicle 1 from the traveling lane is prevented. Accordingly, the LDAcontrol unit 172 calculates a new traveling path in which the vehicle 1having traveled to be separated away from the center of the travelinglane travels toward the center of the traveling lane based on thedetection data, the image data, the specified white line, the calculatedradius of curvature R, the calculated lateral position X, the calculatedlateral velocity V1, the calculated departure angle θ, and the setallowable departure distance D. At this time, the LDA control unit 172calculates a new traveling path satisfying the restriction of theallowable departure distance D set in Step S23. The LDA control unit 172calculates a yaw rate which is estimated to be generated in the vehicle1 traveling on the calculated new traveling path as a target yaw rateγ_(tgt) (Step S26).

Thereafter, the LDA control unit 172 calculates a yaw moment to beapplied to the vehicle 1 for generating the target yaw rate γ_(tgt) inthe vehicle 1 as a target yaw moment M_(tgt) (Step S27). The target yawmoment M_(tgt) is equivalent to the prevention yaw moment.

Thereafter, the LDA control unit 172 calculates a braking force capableof applying the target yaw moment M_(tgt) to the vehicle 1. In thiscase, the LDA control unit 172 individually calculates the brakingforces which are applied to the front-left wheel 121FL, the rear-leftwheel 121RL, the front-right wheel 121FR, and the rear-right wheel121RR. Thereafter, the LDA control unit 172 calculates pressure commandvalues for designating pressures of the brake fluid required forgenerating the calculated braking forces (Step S28). In this case, theLDA control unit 172 individually calculates the pressure command valuesfor designating the pressures of the brake fluid in the wheel cylinders122FL, 122RL, 122FR, and 122RR.

For example, when it is determined that there is a likelihood that thevehicle 1 will depart from the traveling lane over the white linelocated on the right side in the traveling direction of the vehicle 1,the prevention yaw moment capable of deflecting the vehicle 1 to theleft side in the traveling direction of the vehicle 1 has only to beapplied to the vehicle 1 in order to prevent departure of the vehicle 1from the traveling lane. In this case, when no braking force is appliedto the front-right wheel 121FR and the rear-right wheel 121RR and abraking force is applied to at least one of the front-left wheel 121FLand the rear-left wheel 121RL, or when a relatively small braking forceis applied to at least one of the front-right wheel 121FR and therear-right wheel 121RR and a relatively large braking force is appliedto at least one of the front-left wheel 121FL and the rear-left wheel121RL, a prevention yaw moment capable of deflecting the vehicle 1 tothe left side is applied to the vehicle 1. In a case in which it isdetermined that there is a likelihood that the vehicle 1 will departfrom the traveling lane over the white line on the left side in thetraveling direction of the vehicle 1, when no braking force is appliedto the front-left wheel 121FL and the rear-left wheel 121RL and abraking force is applied to at least one of the front-right wheel 121FRand the rear-right wheel 121RR, or when a relatively small braking forceis applied to at least one of the front-left wheel 121FL and therear-left wheel 121RL and a relatively large braking force is applied toat least one of the front-right wheel 121FR and the rear-right wheel121RR, a prevention yaw moment capable of deflecting the vehicle 1 tothe right side in the traveling direction of the vehicle 1 is applied tothe vehicle 1.

Thereafter, the LDA control unit 172 controls the brake actuator 13based on the pressure command values calculated in Step S28.Accordingly, the braking forces corresponding to the pressure commandvalues are applied to at least one of the front-left wheel 121FL, therear-left wheel 121RL, the front-right wheel 121FR, and the rear-rightwheel 121RR (Step S29). As a result, the prevention yaw moment which isequivalent to the target yaw moment M_(tgt) is applied to the vehicle 1,and thus departure of the vehicle 1 from the traveling lane isprevented.

Thereafter, in a state in which the prevention yaw moment is applied tothe vehicle 1, the data acquiring unit 171 acquires the longitudinalacceleration Gx and the lateral acceleration Gy (Step S30). Thereafter,the LDA limiting unit 173 determines whether abnormality conditionswhich are satisfied when a certain abnormality occurs internally orexternally in the vehicle 1 to which the prevention yaw moment isapplied are satisfied based on the longitudinal acceleration Gx and thelateral acceleration Gy acquired in Step S30 (Step S31). That is, theLDA limiting unit 173 determines whether the longitudinal accelerationGx and the lateral acceleration Gy acquired in Step S30 indicates thatan abnormality occurs in the vehicle 1.

An example of the abnormality conditions will be described below withreference to FIGS. 3A to 3D.

First, FIG. 3A is a graph illustrating a relationship between thelongitudinal acceleration Gx and the lateral acceleration Gy when theprevention yaw moment is applied to the vehicle 1 in which noabnormality occurs (that is, an ideal relationship, in other words, atheoretical or experimental relationship). In the following description,unless particularly described, it is assumed that the “longitudinalacceleration Gx” and the “lateral acceleration Gy” refer to the absolutevalue of the longitudinal acceleration Gx and the absolute value of thelateral acceleration Gy. Specifically, in a period in which theprevention yaw moment is applied to the vehicle 1, the longitudinalacceleration Gx is generated in the vehicle 1 due to application of thebraking force for applying the prevention yaw moment. The lateralacceleration Gy with a magnitude corresponding to the longitudinalacceleration Gx which is generated due to application of the preventionyaw moment is generated in the vehicle 1 due to application of theprevention yaw moment. Particularly, when no abnormality occurs in thevehicle 1, the lateral acceleration Gy substantially matches an idealvalue Gy_ide of the lateral acceleration Gy which is estimated frommotion characteristics of the vehicle 1 to be generated in the vehicle 1due to application of the prevention yaw moment in a state in which alongitudinal acceleration Gx is generated in the vehicle 1 due toapplication of the prevention yaw moment. That is, substantially, thelateral acceleration Gy which is generated due to the prevention yawmoment applied to the vehicle 1 in which no abnormality occurs issubstantially matches the ideal value Gy_ide corresponding to thelongitudinal acceleration Gx (in other words, which can be specifiedfrom the longitudinal acceleration Gx).

Each of a plurality of plot points P in FIG. 3A indicates a sample of acombination of the longitudinal acceleration Gx and the lateralacceleration Gy which are actually detected when the prevention yawmoment is applied to the vehicle 1 in which no abnormality occurs. Asillustrated in FIG. 3A, the lateral acceleration Gy which is actuallydetected has unevenness but the ideal value Gy_ide can be approximatedby a function having the longitudinal acceleration Gx as an argument.Particularly, the ideal value Gy_ide can be approximated by a linearfunction F having the longitudinal acceleration Gx as an argument asillustrated in FIG. 3A. That is, the ideal value Gy_ide can beapproximated by an equation of Gy_ide=F(Gx). Particularly, as can beseen from the graph illustrated in FIG. 3A, since the lateralacceleration Gy is also zero ideally when the longitudinal accelerationGx is zero, the ideal value Gy_ide can be approximated by an equation ofGy_ide=A×Gx (where A is a predetermined proportional coefficient).

On the other hand, when an abnormality occurs in the vehicle 1, there isa high likelihood that the lateral acceleration Gy will be greater thanthe ideal value Gy_ide of the lateral acceleration Gy. An example of theinternal abnormality which is assumed in the first embodiment is anabnormality related to a component or a process affecting behavior ofthe vehicle 1 (an abnormality related to a response gain of the vehicle1). An example of the external abnormality which is assumed in the firstembodiment is an abnormality in which the state of the vehicle 1 isseparated from an originally assumed state due to an externalenvironment (particularly, an external environment which is not assumedwhen performing the lane departure preventing operation, such as asudden strong wind or a gradient of a road surface in the lateraldirection) affecting behavior of the vehicle 1.

In this way, the detected lateral acceleration Gy satisfies therelationship of Gy=F(Gx) when the prevention yaw moment is applied tothe vehicle 1 in which no abnormality occurs, and the detected lateralacceleration Gy does not satisfy the relationship of Gy=F(Gx)(specifically, a relationship of Gy>F(Gx) is satisfied) when theprevention yaw moment is applied to the vehicle 1 in which anabnormality occurs. The fact that the lateral acceleration Gy satisfiesthe relationship of Gy>F(Gx) when applying the prevention yaw moment isapplied to the vehicle 1 in which an abnormality occurs was confirmed byexperiment which was performed by the inventor et al. of the disclosure.

Therefore, in the first embodiment, the LDA limiting unit 173 determineswhether a certain abnormality occurs internally or externally in thevehicle 1 based on the comparison result between the lateralacceleration Gy detected in the period in which the prevention yawmoment is applied and the ideal value Gy_ide which is determineddepending on the longitudinal acceleration Gx detected in the period inwhich the prevention yaw moment is applied. That is, the LDA limitingunit 173 determines whether an abnormality occurs in the vehicle 1 bydetermining whether the lateral acceleration Gy which is actuallydetected is greater than the ideal value Gy_ide.

Here, as described above, unevenness occurs in the lateral accelerationGy which is detected in the period in which the prevention yaw moment isapplied. Accordingly, even when no abnormality occurs in the vehicle 1,there is a likelihood that it will be determined that the lateralacceleration Gy is greater than the ideal value Gy_ide due to unevennessof the actually detected lateral acceleration Gy. As a result, when theLDA limiting unit 173 determines that an abnormality occurs in thevehicle 1 in a case in which the lateral acceleration Gy is merelygreater than the ideal value Gy_ide, the likelihood that it will beerroneously determined that an abnormality occurs in the vehicle 1 whichis not originally abnormal relatively becomes higher. Therefore, in thefirst embodiment, the LDA limiting unit 173 determines whether anabnormality occurs in the vehicle 1 by determining whether the actuallydetected lateral acceleration Gy is greater than the ideal value Gy_ideby a predetermined value α (that is, whether the actually detectedlateral acceleration Gy is greater than a first threshold value Gy_th1corresponding to the addition result of the ideal value Gy_ide and thepredetermined value α. That is, the LDA limiting unit 173 determineswhether an abnormality occurs in the vehicle 1 by determining whetherGy>Gy_th1 is satisfied. Accordingly, the condition of “Gy>Gy_th1” is anabnormality condition which is used in Step S31 in FIG. 2. WhenGy>Gy_th1 is satisfied, the LDA limiting unit 173 determines that anabnormality occurs in the vehicle 1. On the other hand, when Gy>Gy_th1is not satisfied, the LDA limiting unit 173 determines that noabnormality occurs in the vehicle 1.

It is preferable that an appropriate value capable of distinguishing thevehicle 1 in which no abnormality occurs and the vehicle 1 in which anabnormality occurs be set as the predetermined value α in considerationof the relationship between the longitudinal acceleration Gx and thelateral acceleration Gy which are generated in the vehicle 1 in which anabnormality occurs and the longitudinal acceleration Gx and the lateralacceleration Gy which is generated in the vehicle 1 in which anabnormality occurs. The predetermined value α is a specific example ofthe above-mentioned “first predetermined value.”

Three specific examples of the abnormality conditions having differentproperties of the predetermined value α will be described below. Thefollowing three specific examples of the abnormality conditions aremerely examples. Accordingly, an abnormality condition different fromthe following abnormality conditions may be used.

First, FIG. 3B is a graph illustrating a first specific example of theabnormality conditions. As illustrated in FIG. 3B, in the first specificexample, a predetermined value α1 (where α1>0) which is a fixed valueregardless of the longitudinal acceleration Gx is used as thepredetermined value α. Accordingly, in the first specific example, thefirst threshold value Gy_th1 is equal to the ideal value Gy_ide+thepredetermined value α1.

Subsequently, FIG. 3C is a graph illustrating a second specific exampleof the abnormality conditions. As illustrated in FIG. 3C, in the secondspecific example, a predetermined value α2 (where α2>0) which variesdepending on the longitudinal acceleration Gx is used as thepredetermined value α. Accordingly, in the second specific example, thefirst threshold value Gy_th1 is equal to the ideal value Gy_ide+thepredetermined value α2. FIG. 3C illustrates an example of thepredetermined value α2 which increases monotonously with an increase ofthe longitudinal acceleration Gx. Here, the predetermined value α2 maydecrease monotonously with an increase of the longitudinal accelerationGx. The predetermined value α2 may vary in an arbitrary mode dependingon the longitudinal acceleration Gx. The predetermined value α2 may bespecified by a function F′ having the longitudinal acceleration Gx as anargument. That is, the predetermined value α2 may be specified by afunction of α2=F′(Gx).

Subsequently, FIG. 3D is a graph illustrating a third specific exampleof the abnormality conditions. As illustrated in FIG. 3D, in the thirdspecific example, a predetermined value α3 (where α3>1) which is a fixedvalue regardless of the longitudinal acceleration Gx is used as aparameter for determining the predetermined value α, other than thepredetermined value α as it is. Here, the predetermined value α3 isdifferent from the predetermined value α1 which is added to the idealvalue Gy_ide to determine the first threshold value Gy_th1 in that thepredetermined value α3 is multiplied by the ideal value Gy_ide todetermine the first threshold value Gy_th1. Accordingly, in the thirdspecific example, the first threshold value Gy_th1 is equal to the idealvalue Gy_ide×the predetermined value α3. In the third specific example,as illustrated in FIG. 3D, the LDA limiting unit 173 also uses theabnormality condition of “Gy>Gy_ide+α (where the predetermined value αis determined by the predetermined value α3).” Similarly to thepredetermined value α2, the predetermined value α3 may be a valuevarying depending on the longitudinal acceleration Gx.

Referring to FIG. 2 again, when it is determined in Step S31 that theabnormality condition is satisfied (YES in Step S31), the LDA limitingunit 173 determines that application of the prevention yaw moment isstopped (Step S32). As a result, the LDA control unit 172 stopsapplication of the braking force capable of applying the prevention yawmoment to the vehicle 1 to the vehicle 1. That is, the LDA control unit172 controls the brake actuator 13 such that the braking force capableof applying the prevention yaw moment to the vehicle 1 is not applied.

After stopping application of the prevention yaw moment, the ECU 17 endsthe lane departure preventing operation illustrated in FIG. 2. When thelane departure preventing operation illustrated in FIG. 2 is ended afterapplication of the prevention yaw moment is stopped, the ECU 17preferably starts the lane departure preventing operation illustrated inFIG. 2 again after the above-mentioned first predetermined period oftime elapses.

On the other hand, when it is determined in Step S31 that theabnormality condition is not satisfied (NO in Step S31), the LDAlimiting unit 173 determines that application of the prevention yawmoment is not stopped. As a result, the LDA control unit 172 continuesto apply the braking force capable of applying the prevention yaw momentto the vehicle 1 to the vehicle 1. Thereafter, the ECU 17 ends the lanedeparture preventing operation illustrated in FIG. 2. When the lanedeparture preventing operation illustrated in FIG. 2 is ended withoutstopping application of the prevention yaw moment, the ECU 17 starts thelane departure preventing operation illustrated in FIG. 2 again afterthe above-mentioned first predetermined period of time elapses. That is,the lane departure preventing operation is started again with theprevention yaw moment applied to the vehicle 1. In this case, when it isdetermined in Step S24 of the lane departure preventing operation whichhas been started again that the prevention yaw moment is applied to thevehicle 1 but there is still a likelihood that the vehicle 1 will departfrom the traveling lane (YES in Step S24), the prevention yaw momentcontinues to be applied by repeatedly performing the operations of StepS25 and the steps subsequent thereto (a case in which the operation ofStep S32 is performed thereafter is excluded). On the other hand, whenit is determined in Step S24 of the lane departure preventing operationwhich has been started again that there is no likelihood that thevehicle 1 will depart from the traveling lane due to application of theprevention yaw moment to the vehicle 1 (NO in Step S24), the lanedeparture preventing operation illustrated in FIG. 2 is ended afterapplication of the prevention yaw moment is ended.

As described above, the LDA limiting unit 173 can determine whether anabnormality occurs in the vehicle 1 based on the differences between thelongitudinal acceleration Gx and the lateral acceleration Gy when anabnormality occurs in the vehicle 1 and the longitudinal acceleration Gxand the lateral acceleration Gy when no abnormality occurs in thevehicle 1. When it is determined that an abnormality occurs in thevehicle 1, the LDA control unit 172 can stop application of theprevention yaw moment. Accordingly, behavior of the vehicle 1 is notdestabilized due to continuous application of the prevention yaw momentwith an abnormality occurring in the vehicle 1. Application of theprevention yaw moment is stopped, and thus the ECU 17 can specify whatabnormality occurs without being affected by application of theprevention yaw moment.

A device according to a first comparative example (so-called electricpower steering (EPS)-LDA) that applies a prevention yaw moment bysteering the turning wheels is known as the lane departure preventingdevice. However, the device according to the first comparative exampledoes not apply a braking force and thus the longitudinal acceleration Gxdue to the prevention yaw moment is not generated in the vehicle.Accordingly, in the device according to the first comparative example,the longitudinal acceleration Gx and the lateral acceleration Gy in asituation in which no abnormality occurs in the vehicle 1 do not satisfya relationship that the lateral acceleration Gy matches the ideal valueGy_ide varying linearly with respect to the longitudinal accelerationGx. That is, in the device according to the first comparative example,it is not possible to determine whether an abnormality occurs in thevehicle by determining whether the lateral acceleration Gy is greaterthan the ideal value Gy_ide by the predetermined value α. A deviceaccording to a second comparative example (specifically, a vehiclestability control device, that is, a so-called vehicle stability control(VCS) device) that prevents a lateral slip of a vehicle is known as adevice that controls a vehicle by applying a braking force to vehiclewheels. However, the device according to the second comparative exampleis a device that applies a braking force in a traveling state in which aslip force of the vehicle wheels exceeds a tire limit (that is, thevehicle wheels start a slip). Accordingly, the longitudinal accelerationGx and the lateral acceleration Gy in a situation in which noabnormality occurs in the vehicle 1 do not satisfy a relationship thatthe lateral acceleration Gy matches the ideal value Gy_ide varyinglinearly with respect to the longitudinal acceleration Gx. That is, therelationship that the lateral acceleration Gy matches the ideal valueGy_ide varying linearly with respect to the longitudinal acceleration Gxis a relationship specific to the vehicle 1 according to the firstembodiment that applies the prevention yaw moment by applying a brakingforce. In view of attention paid to the relationship specific to thevehicle 1 according to the first embodiment that applies the preventionyaw moment by applying the braking force, the vehicle 1 according to thefirst embodiment is much different from the devices according to thefirst and second comparative examples and can exhibit theabove-mentioned remarkable advantages.

In the above description, when it is determined that the abnormalitycondition is satisfied, the LDA control unit 172 stops application ofthe braking force for applying the prevention yaw moment. However, theLDA control unit 172 may set the actually applied braking force to besmaller than the braking force (that is, the target braking force whichshould be originally applied) capable of applying the prevention yawmoment instead of stopping application of the braking force. That is,the LDA control unit 172 may continue to apply the braking force to thevehicle 1 while setting the braking force which is actually applied tobe smaller than the target braking force. In this case, behavior of thevehicle 1 is not destabilized by continuously applying a relativelylarge braking force to apply the prevention yaw moment with anabnormality occurring in the vehicle 1. The operation of stoppingapplication of the braking force is equivalent to the operation ofdecreasing the braking force to zero.

(2) Second Embodiment

A second embodiment will be described below. The second embodiment isdifferent from the first embodiment in that a part of a lane departurepreventing operation is different. Accordingly, the lane departurepreventing operation according to the second embodiment will bedescribed below with reference to FIG. 4. The same processes as theprocesses of the lane departure preventing operation according to thefirst embodiment will be referenced by the same step numbers anddetailed description thereof will not be repeated.

As illustrated in FIG. 4, in the second embodiment, the processes ofSteps S10 to S27 are also performed.

In the second embodiment, after the target yaw moment M_(tgt) iscalculated in Step S27, the LDA limiting unit 173 estimates alongitudinal acceleration Gx and a lateral acceleration Gy which aregenerated in the vehicle 1 when it is assumed that the target yaw momentM_(tgt) calculated in Step S27 is applied to the vehicle 1 (Step S40).Specifically, the LDA limiting unit 173 specifies the currentlongitudinal acceleration Gx and the current lateral acceleration Gy ofthe vehicle 1 (or another arbitrary index capable of specifying thevehicle state) from the detection data acquired in Step S10, andcalculates the longitudinal acceleration Gx and the lateral accelerationGy when the target yaw moment M_(tgt) is applied to the vehicle 1 whichtravels with the specified longitudinal acceleration Gx and thespecified lateral acceleration Gy using a simulation model simulatingthe vehicle 1 or an arbitrary calculation method derived from thesimulation model.

Thereafter, the LDA limiting unit 173 determines whether an abnormalitycondition is satisfied based on the longitudinal acceleration Gx and thelateral acceleration

Gy estimated in Step S40 (Step S41). The abnormality condition used inStep S41 is the same as the abnormality condition used in Step S31 inFIG. 2. The second embodiment is different from the first embodiment inwhich it is determined whether the abnormality condition is satisfiedbased on the longitudinal acceleration Gx and the lateral accelerationGy actually generated in the vehicle 1 after the prevention yaw momentis applied to the vehicle 1, in that before the prevention yaw moment isapplied to the vehicle 1, the longitudinal acceleration Gx and thelateral acceleration Gy which will be generated in the vehicle 1 whenthe prevention yaw moment will be applied to the vehicle 1 are estimatedand it is determined whether the abnormality condition is satisfiedbased on the estimated longitudinal acceleration Gx and the estimatedlateral acceleration Gy.

When it is determined in Step S41 that the abnormality condition issatisfied (YES in Step S41), the LDA limiting unit 173 determines thatapplication of the prevention yaw moment is not started. As a result,the LDA control unit 172 does not start application of a braking forcecapable of applying the prevention yaw moment to the vehicle 1 to thevehicle 1. That is, the LDA control unit 172 controls the brake actuator13 such that the braking force capable of applying the prevention yawmoment to the vehicle 1 is not applied.

On the other hand, when it is determined in Step S41 that theabnormality condition is not satisfied (NO in Step S41), the LDAlimiting unit 173 determines that application of the prevention yawmoment is started. Accordingly, the LDA control unit 172 calculatespressure command values (Step S28) and controls the brake actuator 13based on the calculated pressure command values. Accordingly, brakingforces based on the pressure command values are applied to at least oneof the front-left wheel 121FL, the rear-left wheel 121RL, thefront-right wheel 121FR, and the rear-right wheel 121RR (Step S29).

As described above, according to the second embodiment, the sameadvantages as the advantages which can be achieved in the firstembodiment can be achieved. In the second embodiment, before theprevention yaw moment is actually applied, it is determined whether theabnormality condition is satisfied when it is assumed that theprevention yaw moment is applied. Accordingly, in the second embodiment,the likelihood that the abnormality condition will be satisfied afterthe prevention yaw moment is applied is lower than that in the firstembodiment. As a result, it is possible to further appropriately preventdestabilization in behavior of the vehicle 1 due to continuousapplication of the prevention yaw moment with an abnormality occurringin the vehicle 1.

(3) Third Embodiment

A third embodiment will be described below. The third embodiment isdifferent from the second embodiment in that a part of a lane departurepreventing operation is different. Accordingly, the lane departurepreventing operation according to the third embodiment will be describedbelow with reference to FIG. 5. The same processes as the processes ofthe lane departure preventing operation according to the secondembodiment will be referenced by the same step numbers and detaileddescription thereof will not be repeated.

As illustrated in FIG. 5, in the third embodiment, the processes ofSteps S10 to S27 are also performed, similarly to the second embodiment.

In the third embodiment, after the target yaw moment M_(tgt) iscalculated in

Step S27, the data acquiring unit 171 acquires a current lateralacceleration Gy (Step S51). Hereinafter, the lateral acceleration Gyacquired in Step S51 is referred to as a “lateral acceleration Gy0.”Thereafter, the LDA limiting unit 173 estimates a longitudinalacceleration Gx and a lateral acceleration Gy which are generated in thevehicle 1 when it is assumed that the target yaw moment M_(tgt)calculated in Step S27 is applied to the vehicle 1 (Step S40).

Thereafter, the LDA limiting unit 173 determines whether an abnormalitycondition is satisfied based on the longitudinal acceleration Gx and thelateral acceleration Gy estimated in Step S41 (Step S52). Theabnormality condition used in Step S52 is different from the abnormalitycondition used in the second embodiment in that a second threshold valueGy_th2 is used instead of the first threshold value Gy_th1. The secondthreshold value Gy_th2 is determined depending on the lateralacceleration Gy0 acquired in Step S51. The abnormality condition in thethird embodiment will be described below with reference to FIG. 6.

As illustrated in FIG. 6, the second threshold value Gy_th2 forspecifying the abnormality condition in the third embodiment is acquiredby adding the lateral acceleration Gy0 acquired in Step S51 in FIG. 5 tothe first threshold value Gy th1 for specifying the abnormalitycondition in the second embodiment. That is, the second threshold valueGy_th2 can be specified by an expression of second threshold valueGy_th2=first threshold value Gy_th1+lateral acceleration Gy0=ideal valueGy_ide+predetermined value α+lateral acceleration Gy0. The“predetermined value α+lateral acceleration Gy0” is a specific exampleof the above-mentioned “second predetermined value.” The reason forusing the second threshold value Gy_th2 is as follows.

First, when the lateral acceleration Gy0 is not zero, it is estimatedthat the lateral acceleration Gy is already generated in the vehicle 1in a stage in which the prevention yaw moment is not applied to thevehicle 1 yet. In the following description, a situation in which thevehicle 1 is turning is assumed as the situation in which the lateralacceleration Gy is already generated in the vehicle 1 in the stage inwhich the prevention yaw moment is not applied to the vehicle 1 yet.Examples of the situation in which the lateral acceleration Gy isalready generated in the vehicle 1 in the stage in which the preventionyaw moment is not applied to the vehicle 1 yet include a situation inwhich a lateral wind blows in the vehicle 1 and a situation in which thevehicle 1 travels on a road surface inclined in the lateral direction.In this case, the lateral acceleration Gy estimated in Step S40 in FIG.5 includes a component of the lateral acceleration Gy (that is, thelateral acceleration Gy due to turning of the vehicle 1) which isalready generated before the prevention yaw moment is applied as well asa component of the lateral acceleration Gy which is generated due toapplication of the prevention yaw moment. This is because, as describedabove, the LDA limiting unit 173 specifies the current longitudinalacceleration Gx and the current lateral acceleration Gy (that is, thelateral acceleration Gy substantially equivalent to the lateralacceleration Gy 0) of the vehicle 1 and calculates the longitudinalacceleration Gx and the lateral acceleration Gy when the prevention yawmoment is applied to the vehicle 1 traveling with the specifiedlongitudinal acceleration Gx and the specified lateral acceleration Gybased on the prevention yaw moment.

Although the same prevention yaw moment is applied, the lateralacceleration Gy (see point P1 in FIG. 6) estimated when the vehicle 1 isturning is greater than the lateral acceleration Gy (see point P2 inFIG. 6) estimated when the vehicle 1 travels straightly by the lateralacceleration Gy0. Accordingly, even when no abnormality occurs in thevehicle 1, there is a likelihood that it will be erroneously determinedthat the lateral acceleration Gy which is greater than the lateralacceleration Gy originally generated due to application of theprevention yaw moment by the lateral acceleration Gy0 is greater thanthe first threshold value Gy_th1. That is, even when no abnormalityoccurs in the vehicle 1, there is a likelihood that it will beerroneously determined that the abnormality condition is satisfied dueto turning of the vehicle 1.

Therefore, in the third embodiment, in consideration of a point that thelateral acceleration Gy0 already generated before the prevention yawmoment is applied can be included in the lateral acceleration Gyestimated by the LDA limiting unit 173, the second threshold valueGy_th2 is greater than the first threshold value Gy_th1 by the lateralacceleration Gy0. Accordingly, even when the lateral acceleration Gy0already generated before the prevention yaw moment is applied isincluded in the lateral acceleration Gy estimated by the LDA limitingunit 173, the above-mentioned erroneous determination is not caused.

When the lateral acceleration Gy0 is zero, the second threshold valueGy_th2 is equal to the first threshold value Gy_th1. Accordingly, whenthe lateral acceleration Gy0 is zero, the same processes as in thesecond embodiment are performed in the third embodiment. That is, in thethird embodiment, substantially, it is determined whether the estimatedlateral acceleration Gy is greater than the second threshold valueGy_th2 when application of the prevention yaw moment is started in thestate in which the lateral acceleration Gy0 is generated in the vehicle1, and it is determined whether the estimated lateral acceleration Gy isgreater than the first threshold value Gy_th1 when application of theprevention yaw moment is started in the state in which the lateralacceleration Gy0 is not generated in the vehicle 1 (that is, the lateralacceleration Gy0 is zero).

Referring to FIG. 5 again, when it is determined in Step S52 that theabnormality condition is satisfied (YES in Step S52), the LDA limitingunit 173 determines that application of the prevention yaw moment is notstarted. As a result, the LDA control unit 172 controls the brakeactuator 13 such that the braking force capable of applying theprevention yaw moment to the vehicle 1 is not applied. On the otherhand, when it is determined in Step S52 that the abnormality conditionis not satisfied (NO in Step S52), the LDA limiting unit 173 determinesthat application of the prevention yaw moment is started. Accordingly,the LDA control unit 172 calculates the pressure command values (StepS28) and controls the brake actuator 13 based on the calculated pressurecommand values. Accordingly, the braking forces corresponding to thepressure command values are applied to at least one of the front-leftwheel 121FL, the rear-left wheel 121RL, the front-right wheel 121FR, andthe rear-right wheel 121RR (Step S29).

As described above, according to the third embodiment, the sameadvantages as the advantages which can be achieved in the secondembodiment can be achieved. In the third embodiment, even when thelateral acceleration Gy0 is already generated in the vehicle 1 beforethe prevention yaw moment is applied, it is possible to appropriatelydetermine whether an abnormality occurs in the vehicle 1.

In the first embodiment, there is a likelihood that the lateralacceleration Gy0 (for example, the lateral acceleration due to turningwhich is generated in a situation in which the vehicle 1 to which theprevention yaw moment is applied turns) already generated before theprevention yaw moment is applied will be included in the lateralacceleration Gy (Step S30 in FIG. 2) acquired by the data acquiring unit171 to determine whether the abnormality condition is satisfied.Accordingly, in the first embodiment, the abnormality condition which isspecified by the second threshold value Gy_th2 instead of the firstthreshold value Gy_th1 may be used. In this case, similarly to the thirdembodiment, it is preferable that the lateral acceleration Gy0 beacquired before the prevention yaw moment is applied in the firstembodiment.

In the second and third embodiments, similarly to the first embodiment,when it is determined that the abnormality condition is satisfied, theLDA control unit 172 may start application of a braking force smallerthan the braking force (that is, a target braking force which should beoriginally applied) capable of applying the prevention yaw moment may bestarted instead of applying the braking force for applying theprevention yaw moment.

At least a part of the elements of the first to third embodiments may beappropriately combined with another part of the elements of the first tothird embodiments. At least a part of the elements of the first to thirdembodiments may not be used.

The disclosure can be appropriately modified without departing from thegist or spirit of the disclosure which can be read from the claims andthe whole specification, and a lane departure preventing deviceincluding such modifications is included in the technical spirit of thedisclosure.

What is claimed is:
 1. A lane departure preventing device comprising atleast one electronic control unit configured to: when there is alikelihood that a vehicle will depart from a traveling lane in which thevehicle travels, calculate a prevention yaw moment, the prevention yawmoment for preventing departure of the vehicle from the traveling lane,and control a brake actuator configured to apply a braking force to avehicle wheel such that the prevention yaw moment is applied to thevehicle; acquire a first lateral acceleration and a longitudinalacceleration, the first lateral acceleration and the longitudinalacceleration being generated in the vehicle when the prevention yawmoment is applied; determine whether the first lateral acceleration isgreater than an estimated value of the first lateral acceleration by afirst predetermined value, the estimated value of the first lateralacceleration being estimated, from motion characteristics of thevehicle, to be generated in the vehicle due to application of theprevention yaw moment when the longitudinal acceleration is generated inthe vehicle due to application of the prevention yaw moment; and controlthe brake actuator such that the braking force is less than a targetbraking force, the target braking force being required to apply theprevention yaw moment to the vehicle, when it is determined that thefirst lateral acceleration is greater than the estimated value by thefirst predetermined value.
 2. The lane departure preventing deviceaccording to claim 1, wherein the at least one electronic control unitis configured to cancel application of the braking force by the brakeactuator when it is determined that the first lateral acceleration isgreater than the estimated value by the first predetermined value. 3.The lane departure preventing device according to claim 1, wherein theat least one electronic control unit is configured to: determine whethera total value of the first lateral acceleration and a second lateralacceleration is greater than the estimated value by a secondpredetermined value, the second predetermined value being greater thanthe first predetermined value, when application of the prevention yawmoment is started in a state in which the second lateral acceleration isgenerated in the vehicle; determine whether the first lateralacceleration is greater than the estimated value by the firstpredetermined value when application of the prevention yaw moment isstarted in a state in which the second lateral acceleration is notgenerated in the vehicle; control the brake actuator such that thebraking force matches the target braking force when it is determinedthat the total value of the first lateral acceleration and the secondlateral acceleration is not greater than the estimated value by thesecond predetermined value; and control the brake actuator such that thebraking force is less than the target braking force when it isdetermined that the total value of the first lateral acceleration andthe second lateral acceleration is greater than the estimated value bythe second predetermined value.
 4. The lane departure preventing deviceaccording to claim 3, wherein the second predetermined value is greaterthan the first predetermined value by the second lateral acceleration,and the second lateral acceleration is generated in the vehicle beforeapplication of the prevention yaw moment is started.
 5. The lanedeparture preventing device according to claim 3, wherein the at leastone electronic control unit is configured to cancel application of thebraking force by the brake actuator when it is determined that the totalvalue of the first lateral acceleration and the second lateralacceleration is greater than the estimated value by the secondpredetermined value.
 6. The lane departure preventing device accordingto claim 1, wherein the first predetermined value is calculated based onthe longitudinal acceleration.
 7. The lane departure preventing deviceaccording to claim 1, wherein the at least one electronic control unitis configured to determine whether the first lateral acceleration isgreater than a first threshold value that is greater than the estimatedvalue by the first predetermined value.
 8. The lane departure preventingdevice according to claim 1, wherein the first predetermined value is afixed value.
 9. The lane departure preventing device according to claim1, wherein the first predetermined value varies based on thelongitudinal acceleration.
 10. A lane departure preventing devicecomprising: at least one electronic control unit configured to: whenthere is a likelihood that a vehicle will depart from a traveling lanein which the vehicle travels, calculate a prevention yaw moment, theprevention yaw moment for preventing departure of the vehicle from thetraveling lane, and control a brake actuator configured to apply abraking force to a vehicle wheel such that the prevention yaw moment isapplied to the vehicle; acquire a first lateral acceleration and alongitudinal acceleration, the first lateral acceleration and thelongitudinal acceleration being generated in the vehicle when theprevention yaw moment is applied; determine whether the first lateralacceleration is greater than a first threshold value that is greaterthan an estimated value of the first lateral acceleration by a firstpredetermined value, the estimated value of the first lateralacceleration being estimated, from motion characteristics of thevehicle, to be generated in the vehicle due to application of theprevention yaw moment when the longitudinal acceleration is generated inthe vehicle due to application of the prevention yaw moment; and controlthe brake actuator such that the braking force is less than a targetbraking force, the target braking force being required to apply theprevention yaw moment to the vehicle, when it is determined that thefirst lateral acceleration is greater than the first threshold value.11. A lane departure preventing device comprising: at least oneelectronic control unit configured to: when there is a likelihood that avehicle will depart from a traveling lane in which the vehicle travels,calculate a prevention yaw moment, the prevention yaw moment forpreventing departure of the vehicle from the traveling lane, and controla brake actuator configured to apply a braking force to a vehicle wheelsuch that the prevention yaw moment is applied to the vehicle; acquire afirst lateral acceleration and a longitudinal acceleration, the firstlateral acceleration and the longitudinal acceleration being generatedin the vehicle when the prevention yaw moment is applied; determinewhether the first lateral acceleration is greater than a first thresholdvalue that corresponds to a sum of an estimated value of the firstlateral acceleration and a first predetermined value, the estimatedvalue of the first lateral acceleration being estimated, from motioncharacteristics of the vehicle, to be generated in the vehicle due toapplication of the prevention yaw moment when the longitudinalacceleration is generated in the vehicle due to application of theprevention yaw moment; and control the brake actuator such that thebraking force is less than a target braking force, the target brakingforce being required to apply the prevention yaw moment to the vehicle,when it is determined that the first lateral acceleration is greaterthan the first threshold value, wherein the first threshold value isdifferent than the estimated value.